THE BONES OF THE LOWER LIMB 



253 



the peroneus longus, and the lower two-thirds, except the last 

 2 inches, to the peroneus brevis, these two muscles overlapping 

 towards the centre of the bone. 



The medullary foramen, which is small, is usually situated on the 

 posterior surface, but may be on the internal, a little above the 

 centre, and there may be an additional one a little higher up. It is 

 for a branch of the peroneal artery, and the direction of the foramen 

 and the canal to which it leads is downwards towards the ankle. 



Articulations. — Superiorly with the external tuberosity of the 

 tibia, and inferiorly with the outer aspect of the tibia, and the ex- 

 ternal surface of the astragalus. 



Structure. — ^The structure is that of a long bone, and the marrow 

 canal is limited to about the middle three-fifths of the shaft. 



^ 



Appears about the 4th Year, 

 and joins about 23 



|l.. Appears in the 8th Week 

 (intra-uterine) 



Ossification. — The fibula ossifies in cartilage from one primary, and two 

 secondary, centres. The primaiy centre for the shaft appears in the eighth 

 week of intra-uterine Ufe. At birth the shaft 

 is ossified, but the extremities are cartilaginous. 

 The centre for the lower extremity appears in 

 the second year, and that for the upper extremity 

 about the fourth year. The lower epiphysis 

 joins the shaft about twenty, and the upper 

 about twenty-three. The fibula forms an excep- 

 tion to the general law of ossification apphcable 

 to long bones with an epiphysis, or epiphyses, at 

 either end, which may be here restated as 

 follows : ' The epiphysis or epiphyses, at the end 

 towards which the medullary foramen and the 

 canal to which it leads are directed, are the last to 

 show signs of ossification, but they are the first to 

 join the shaft.' In the fibula the lower epiphysis 

 not only joins the shaft first, but it is the first to 

 show signs of ossification — due to the fact that 

 this extremity is the least rudimentary part 

 of the bone. 



At about the seventh month of intrauterine 



hfe the tibial and fibular malleoh are of nearly 



equal proportions, but by the second year. 



previous to the appearance of its centre of 



ossification, the fibular malleolus hcis attained 



the large relative size which characterizes it throughout Ufe. 



Fig. 



Appears m the 2nd Year, 



and joins about 20 



148. — Ossification of 

 THE Fibula. 



The Tarsus. 



The tarsus is composed of seven short bones, namely, the 

 astragalus, os calcis, navicular or scaphoid, three cuneiforms, and 

 cuboid. 



The first two constitute the proximal row, the astragalus l5dng 

 above the os calcis, and the last four comprise the distal row, the 

 order from the inner or tibial to the outer or fibular side being in- 

 ternal, middle, and external cuneiform bones, and cuboid. The 

 navicular occupies an intermediate position. 



